Controls and operation of variable frequency drives

ABSTRACT

A system includes a refrigerant circuit including a compressor, a condenser, an expander, an electric motor configured to drive the compressor, and a controller configured to control a motor drive to drive the electric motor. The controller is configured to first evaluate whether the compressor is idle based upon a control state of the controller being configured not to operate the motor drive to drive the motor, second, in response to an affirmative evaluation that the compressor is idle, evaluate a risk of undesired or un-commanded compressor rotation based upon a combination of two or more system conditions, each of the two or more system conditions indicating the risk of undesired or un-commanded compressor rotation, and third, in response to an affirmative evaluation of the risk of undesired or un-commanded compressor rotation, control the motor drive to oppose rotation of the compressor.

BACKGROUND

The present application relates generally to controls and operation ofvariable frequency drives and more particularly, but not exclusively tocontrols and operation of variable frequency drives in connection withheating, cooling, air-conditioning and/or refrigeration (“HVACR”)systems. In such systems, undesired, un-commanded or uncontrolledcompressor rotation, for example, reverse rotation of a screw or scrollcompressor, poses substantial issues. Mitigating the potential for suchoccurrences remains an area of interest as present approaches to thissuffer from a variety of limitations and disadvantages. Undesired,uncontrolled or un-commanded compressor operation may result in damageto system components either in the form of abrupt failure or increasedwear and tear. These issues may be of particular interest in HVACRapplications including compressors driven by electric motors which arein turn driven by variable frequency drives. There is a significant needfor the unique and inventive apparatuses, methods and systems disclosedherein.

SUMMARY

One embodiment is a system comprising a refrigerant circuit including acompressor configured to compress refrigerant, a condenser configured toreceive refrigerant from the compressor, and an expander configured toreceive refrigerant from the condenser; an electric motor configured todrive the compressor; a power supply configured to drive the electricmotor; and a controller configured to control the power supply to drivethe electric motor and analyze at least one system condition; whereinthe controller is configured to identify a condition associated withrisk of undesired or un-commanded compressor rotation based upon the atleast one system condition and control the power supply to opposerotation of the compressor based upon the identification of thecondition. In some forms the controller being configured to control thepower supply to oppose rotation of the compressor comprises thecontroller being configured to control the power supply to provide ashort circuit condition effective to provide an electrical resistance tocurrent generated by rotation of the motor. In some forms the shortcircuit condition comprises two or more switching devices of the powersupply being closed to provide a short circuit. In some forms the shortcircuit condition comprises providing a closed circuit including two ormore windings of the motor and a rail of the power supply.

In some forms the controller being configured to control the powersupply to oppose rotation of the compressor comprises the controllerbeing configured to control the power supply to provide a DC current tothe motor effective to urge the motor to a predetermined alignment andresist rotation of the motor. In some forms the controller beingconfigured to identify a condition associated with risk of undesired orun-commanded compressor rotation based upon the at least one systemcondition comprises identifying a pressure differential across thecompressor associated with risk of undesired or un-commanded compressorrotation. In some forms the controller being configured to identify acondition associated with risk of undesired or un-commanded compressorrotation based upon the at least one system condition comprisesidentifying an idle condition of the compressor and a pressure conditionassociated with risk of undesired or un-commanded compressor rotation.In some forms the controller being configured to identify a conditionassociated with risk of undesired or un-commanded compressor rotationbased upon the at least one system condition comprises first identifyingwhether the compressor is commanded not to operate and secondidentifying a pressure condition associated with risk of undesired orun-commanded compressor rotation.

In some forms the power supply comprises an inverter. In some forms thepower supply comprises a variable frequency drive. In some forms thecondition associated with risk of undesired or un-commanded compressorrotation comprises rotation of a rotor of the motor. In some forms thecondition associated with risk of undesired or un-commanded compressorrotation comprises rotation of the compressor being detected with asensor. In some forms the condition associated with risk of undesired orun-commanded compressor rotation comprises back EMF indicative ofrotation being detected at a motor terminal.

One embodiment is a method comprising providing an HVACR systemincluding an electrical drive configured to drive an electric motor, acompressor configured to be driven by the electric motor, and acontroller configured to control output of the drive and analyze acondition of the system; identifying a system condition associated withrisk of undesired or un-commanded compressor rotation; controlling thedrive to electrically oppose rotation of the motor effective to opposerotation of the compressor. In some forms the act of controlling thedrive to electrically oppose rotation of the motor comprises controllingthe drive to provide a current to the motor effective to force the motortoward a predetermined position. In some forms the magnitude of thecurrent is selected to provide force sufficient to resist forceattributable to the system condition associated with risk of undesiredor un-commanded compressor rotation. In some forms the act ofcontrolling the drive to electrically oppose rotation of the motorcomprises controlling the drive to provide a closed circuit includingtwo or more windings of the electric motor and including an electricalresistance effective to resist rotation of the motor based upondissipation of current induced in the motor by rotation. In some formsthe closed circuit further includes two or more switches of the driveand one or more rails of the drive.

In some forms the act of identifying a system condition associated withrisk of undesired or un-commanded compressor rotation includesidentifying a pressure condition at least one of upstream and downstreamof the compressor. In some forms the act of identifying a systemcondition associated with risk of undesired or un-commanded compressorrotation includes identifying a pressure differential across thecompressor. In some forms the act of identifying a system conditionassociated with risk of undesired or un-commanded compressor rotationincludes identifying whether the compressor is in an idle state. In someforms the act of identifying a system condition associated with risk ofundesired or un-commanded compressor rotation includes identifyingwhether the compressor is in an idle state and identifying a pressurecondition associated with the compressor. In some forms the act ofidentifying a system condition associated with risk of undesired orun-commanded compressor rotation includes first determining whether thedrive, the motor or the compressor is in a non-operational state, andsecond determining a pressure condition associated with risk ofundesired or un-commanded compressor rotation. In some forms the act ofidentifying a system condition associated with risk of undesired orun-commanded compressor rotation comprises detecting rotation of themotor with a sensor. In some forms the act of identifying a systemcondition associated with risk of undesired or un-commanded compressorrotation comprises detecting rotation of the compressor. In some formsthe act of identifying a system condition associated with risk ofundesired or un-commanded compressor rotation comprises detecting backEMF or a current induced by back EMF indicative of rotation at a motorterminal.

One embodiment is a method for starting a compressor in a refrigerantloop, comprising operating the compressor in a first mode which includespreventing current level for a motor of the compressor from exceeding apredetermined current limit for a period of time not to exceed apredetermined period of time and determining if the motor exceeds apredetermined speed threshold at or before expiration of thepredetermined period of time. Some forms further comprise operating thecompressor in a second mode in response to determining the motor hasexceeded the predetermined speed threshold at or before expiration ofthe predetermined period of time. In some forms operation of thecompressor in the second mode includes increased motor speed relative tooperation of the compressor in the first mode. Some forms furthercomprise stopping operation of the compressor in response to determiningthe motor has failed to exceed the predetermined speed threshold at orbefore expiration of the predetermined period of time. In some forms thecompressor is a screw compressor. In some forms operation of thecompressor in the first mode is performed in response to determiningmotor torque exceeds a predetermined value. Some forms further comprisemeasuring motor current and using the measured motor current todetermine motor torque. In some forms operation of the compressor in thefirst mode is automatically performed upon starting the compressor. Insome forms the predetermined current limit and the predetermined periodof time are selected to provide a liquid clearing function withoutdamage to the compressor. In some forms preventing the current level forthe motor of the compressor from exceeding the predetermined currentlimit includes limiting voltage supplied to the motor.

One embodiments is a system comprising a refrigerant compressorincluding an electric motor and a controller configured to operate thecompressor in a start mode where current of the motor is prevented fromexceeding a predetermined current limit for a period of time not toexceed a predetermined period of time, and to operate the compressor ina run mode in response to determining the motor exceeds a predeterminedspeed threshold at or before expiration of the predetermined period oftime. In some forms the controller is further configured to stopoperation of the compressor in response to determining the motor failsto reach the predetermined speed threshold at or before expiration ofthe predetermined period of time. In some forms operation of thecompressor in the run mode includes increased motor speed relative tooperation of the compressor in the start mode. In some forms thecontroller is further configured to operate the compressor in the startmode in response to a determination that motor torque exceeds apredetermined value. Some forms further comprise a sensor configured tomeasure motor current and provide a corresponding indication to thecontroller, wherein the controller is further configured to use themeasured motor current to determine motor torque. In some forms thecontroller is further configured to automatically operate the compressorin the start mode upon activation of the compressor. In some forms thepredetermined current limit corresponds to a maximum current rating foroperation of the compressor with the speed of the motor at or under thespeed of the predetermined speed threshold in order to avoid compressordamage. Some forms further comprise a refrigeration loop, a condenser,an evaporator and a variable frequency drive.

One embodiment is a method for operating a refrigerant compressorcomprising following a speed trajectory configured to maintain motorspeed of the compressor from exceeding a predetermined speed limit for apredetermined period of time following start of the compressor andstopping operation of the compressor if motor current of the compressorexceeds a predetermined current limit before expiration of thepredetermined period of time. In some forms the predetermined speedlimit and predetermined period of time are selected to provide a liquidclearing function without damage to the compressor. In some forms thespeed trajectory is further configured to increase motor speed of thecompressor above the predetermined speed limit following expiration ofthe predetermined period of time. In some forms the speed trajectoryincludes a first segment falling within the predetermined period oftime, the first segment including a speed increase period to the speedof the predetermined speed limit following start of the compressor and adwell period at the speed of the predetermined speed threshold untilexpiration of the predetermined period of time. In some forms thecompressor is a screw compressor. In some forms the speed trajectory isautomatically followed upon starting the compressor. In some forms thespeed trajectory is followed in response to determining motor torqueexceeds a predetermined value.

One embodiment is a system comprising a refrigerant compressor includingan electric motor and a controller configured to operate the compressorin a start mode configured to prevent speed of the motor from exceedinga predetermined speed limit for a predetermined period of time followingstart of the compressor, and to stop operation of the compressor ifcurrent of the motor exceeds a predetermined current limit beforeexpiration of the predetermined period of time. In some forms thepredetermined speed limit and predetermined period of time are selectedto provide a liquid clearing function without damage to the compressor.In some forms the controller is further configured to operate thecompressor in a run mode following expiration of the predeterminedperiod of time, the run mode including a higher motor speed relative tothe start mode. In some forms the controller is further configured toautomatically operate the compressor in the start mode followingactivation of the compressor. In some forms the predetermined currentlimit corresponds to a maximum current rating for operation of thecompressor with the speed of the motor at or under the speed of thepredetermined speed limit in order to avoid compressor damage

One embodiment is method comprising supplying current from a drive tostart an electric motor that is mechanically coupled with and configuredto drive a compressor of an HVACR system, the compressor configured tooperate in one direction; determining information indicative of acurrent drawn by said electric motor during a selected time periodduring the supplying; comparing said information to a threshold; andinterrupting operation of the motor if said information exceeds thethreshold. In some forms said act of interrupting comprises terminatingsaid supply of current. In some forms said act of determining comprisesreceiving input from a sensor at a controller input. In some forms saidact of determining comprises converting the input received from thesensor from analog to digital. In some forms the determining occursduring a predetermined time period after the commencement of the act ofsupplying current. In some forms the predetermined time period isselected to occur after an initial time period in which a current spikeis expected. Some forms further comprise continuing said act ofsupplying current to said electric motor after said motor is started ifsaid information does not exceed the threshold.

One embodiments is a system comprising an electric motor drivinglycoupled to a screw or scroll compressor a power supply drivingly coupledto said electric motor; and a controller configured to control the powersupply to selectably supply current to the electric motor, evaluate acharacteristic of the current drawn from the power supply by the motorrelative to a threshold, and control the power supply to cease supplyingcurrent to the electric motor based upon an evaluation that thecharacteristic is greater than the threshold. In some forms thecontroller includes a supply module structured to selectably supplycontinuous current from said power supply to said electric motor. Insome forms the characteristic is a current magnitude. In some forms thecontroller includes a current module structured to interpret a magnitudeof a current drawn by said electric motor during a selected time periodand evaluate said magnitude relative to the threshold. In some forms thepower supply comprises a variable frequency drive. In some forms thethreshold is selected to distinguish a current condition attributable tothe screw or scroll compressor being driven in a reverse direction and acurrent condition attributable to starting of the compressor in aforward direction. In some forms the threshold is selected to be greaterin magnitude than a maximum characteristic value expected when startingthe compressor with the electric motor coupled to the power supply. Insome forms the characteristic value is a current magnitude.

One embodiment is an apparatus comprising a non-transitory computerreadable medium configured with instructions executable by a computer toperform the following acts: command a drive to supply current to anelectric motor in response to a start command; determine acharacteristic of current flowing through the electric motor; comparethe characteristic with one or more predetermined criteria; and commandthe drive to stop supplying current to the electric motor based upon thecharacteristic not meeting at least one of the one or more predeterminedcriteria. In some forms the one or more predetermined criteria comprisea current magnitude limit. In some forms the one or more predeterminedcriteria comprise a limit on integrated current or summed current. Insome forms the one or more predetermined criteria comprise a limit oninstantaneous rate of change of current or a limit on a currentdifferential. In some forms the electric motor comprises one of aninduction motor and a permanent magnet motor. In some forms thecompressor comprises one of a scroll compressor and a screw compressor.It shall be understood that the techniques, methods, controls,diagnostics, and logic disclosed herein may be implemented in a varietyof software, hardware, firmware, and combinations thereof. Furtherembodiments, forms, objects, features, advantages, aspects, and benefitsshall become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary HVACR system.

FIG. 2 is a schematic illustration of an exemplary variable frequencydrive configured to drive an electric motor.

FIG. 3 is a schematic illustration of another exemplary variablefrequency drive configured to drive an electric motor.

FIG. 4 is a flow diagram illustrating an exemplary control process.

FIG. 5 is a graphical illustration of one approach for starting therefrigerant compressor of the system of FIG. 1.

FIGS. 6-7 are graphical illustrations of another approach for startingthe refrigerant compressor of the system of FIG. 1.

FIG. 8 is a graphical illustration of yet another approach for startingthe refrigerant compressor of the system of FIG. 1.

FIG. 9 is a schematic illustration of an exemplary HVACR system.

FIG. 10 is a schematic illustration of an exemplary HVACR system andflow diagram illustrating an exemplary control process.

FIG. 11 is an exemplary graph representing the drawn current feedback ofan exemplary HVACR system.

FIG. 12 is an exemplary graph representing the drawn current feedback ofan exemplary HVACR system.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

For the purposes of clearly, concisely and exactly describing exemplaryembodiments of the invention, the manner and process of making and usingthe same, and to enable the practice, making and use of the same,reference will now be made to certain exemplary embodiments, includingthose illustrated in the figures, and specific language will be used todescribe the same. It shall nevertheless be understood that nolimitation of the scope of the invention is thereby created, and thatthe invention includes and protects such alterations, modifications, andfurther applications of the exemplary embodiments as would occur to oneskilled in the art.

With reference to FIG. 1 there is illustrated an exemplary HVACR system100 which includes a refrigerant loop comprising a compressor 110, acondenser 120, and an evaporator 130. Compressor 110 may be a screwcompressor, a scroll compressor, or another type of compressor which isdesigned to rotate only in one direction. Refrigerant flows throughsystem 100 in a closed loop from compressor 110 to condenser 120 toevaporator 130 and back to compressor 110. Various embodiments may alsoinclude additional refrigerant loop elements including, for example,valves for controlling refrigerant flow, refrigerant filters,economizers, oil separators and/or cooling components and flow paths forvarious system components.

Compressor 110 is driven by a drive unit 150 including a permanentmagnet electric motor 170 which is driven by a variable frequency drive155. In the illustrated embodiment, variable frequency drive 155 isconfigured to output a three-phase PWM drive signal, and motor 170 is asurface magnet permanent magnet motor. Use of other types andconfigurations of variable frequency drives and electric motors such asinterior magnet permanent magnet motors, reluctance motors, orinductance motors are also contemplated. It shall be appreciated thatthe principles and techniques disclosed herein may be applied to a broadvariety of drive and permanent magnet motor configurations.

Condenser 120 is configured to transfer heat from compressed refrigerantreceived from compressor 110. In the illustrated embodiment condenser120 is a water cooled condenser which receives cooling water at an inlet121, transfers heat from the refrigerant to the cooling water, andoutputs cooling water at an output 122. It is also contemplated thatother types of condensers may be utilized, for example, air cooledcondensers or evaporative condensers. It shall further be appreciatedthat references herein to water include water solutions comprisingadditional constituents unless otherwise limited.

Evaporator 130 is configured to receive refrigerant from condenser 120,expand the received refrigerant to decrease its temperature and transferheat from a cooled medium to the refrigerant. In the illustratedembodiment evaporator 130 is configured as a water chiller whichreceives water provided to an inlet 131, transfers heat from the waterto the refrigerant, and outputs chilled water at an outlet 132. It iscontemplated that a number of particular types of evaporators may beutilized, including dry expansion evaporators, flooded type evaporators,bare tube evaporators, plate surface evaporators, and finned evaporatorsamong others.

HVACR system 100 further includes a controller 160 which outputs controlsignals to variable frequency drive 155 to control operation of themotor 170 and compressor 110. Controller 160 also receives informationabout the operation of drive unit 150. In exemplary embodimentscontroller 160 receives information relating to motor current, motorterminal voltage, and/or other operational characteristics of the motor.It shall be appreciated that the controls, control routines, and controlmodules described herein may be implemented using hardware, software,firmware and various combinations thereof and may utilize executableinstructions stored in a non-transitory computer readable medium ormultiple non-transitory computer readable media. It shall further beunderstood that controller 160 may be provided in various forms and mayinclude a number of hardware and software modules and components such asthose disclosed herein.

With reference to FIG. 2 there is illustrated an exemplary circuitdiagram for a variable frequency motor drive 200. Drive 200 is connectedto a power source 210, for example, a 400/480 VAC utility power supplywhich provides three-phase AC power to line filter module 220. Linefilter module 220 is configured to provide harmonic damping to mitigatelosses which can arise from harmonic feedback from drive components topower source 210. Line filter module 220 outputs three-phase AC power toa rectifier 290 which converts the AC power to DC power and provides theDC power to a DC bus 291. DC bus 291 is preferably a filmcapacitor-cased bus which includes one or more film capacitorselectrically coupled between positive and negative bus rails. DC bus 291is connected to inverter 280. For clarity of illustration anddescription, rectifier 290, DC bus 291, and inverter 280 are shown asdiscrete elements. It shall be appreciated, however, that two or more ofthese components may be provided in a common module, board or boardassembly which may also include a variety of additional circuitry andcomponents. It shall be further understood that, in addition to theillustrated 6-pulse rectifier, other multiple pulse rectifiers such as12-pulse, 18-pulse, 24-pulse or 30-pulse rectifiers may be utilizedalong with phase shifting transformers providing appropriate phaseinputs for 6-pulse 12-pulse, 18-pulse, 24-pulse, or 30-pulse operation.

Inverter module 280 includes switches 285, 286 and 287 which areconnected to the positive and negative rails of DC bus 291. Switches285, 286 and 287 are preferably configured as IGBT and diode basedswitches, but may also utilize other types of power electronicsswitching components such as power MOSFETs or other electrical switchingdevices. Switches 285, 286 and 287 provide output to motor terminals275, 276 and 277. Current sensors 281, 282 and 283 are configured todetect current flowing from inverter module 280 to motor 270 and sendcurrent information to ID module 293. Voltage sensors are alsooperatively coupled with motor terminals 275, 276 and 277 and configuredto provide voltage information from the motor terminals to ID module293.

ID module 293 includes burden resistors used in connection with currentsensing to set the scaling on current signals ultimately provided toanalog to digital converters for further processing. ID module 293 tellsthe VFD what size it is (i.e. what type of scaling to use on currentpost ADC) using identification bits which are set in hardware on the IDmodule 293. ID module 293 also outputs current and voltage informationto gate drive module 250 and also provides identification information togate drive module 250 which identifies the type and size of the load towhich gate drive module 250 is connected. ID module 293 may also providecurrent sensing power supply status information to gate drive module250. ID module 293 may also provide scaling functionality for otherparameters such as voltage or flux signals in other embodiments.

Gate drive module 250 provides sensed current and voltage information toanalog to digital converter inputs of DSP module 260. DSP module 260processes the sensed current and voltage information and also providescontrol signals to gate drive module 250 which control signals gatedrive module 250 to output voltages to boost modules 251, 252 and 253,which in turn output boosted voltages to switches 285, 286 and 287. Thesignals provided to switches 285, 286 and 287 in turn control the outputprovided to terminals 275, 276 and 277 of motor 270.

Motor 270 includes a stator 271, a rotor 273, and an air gap 272 betweenthe rotor and the stator. Motor terminals 275, 276 and 277 are connectedto windings provided in stator 271. Rotor 273 includes a plurality ofpermanent magnets 274. In the illustrated embodiment magnets 274 areconfigured as surface permanent magnets positioned about thecircumference of rotor 273. The rotor is typically constructed using thepermanent magnets in such a way as essentially a constant magnetic fluxis present at the surface of the rotor. In operation with rotation ofthe rotor, the electrical conductors forming the windings in the statorare disposed to produce a sinusoidal flux linkage. Other embodimentsalso contemplate the use of other magnet configurations such as interiormagnet configurations, as well as inductance motor configurations,reluctance motor configurations and other non-permanent magnetconfigurations.

With reference to FIG. 3 there is illustrated schematic diagram 300including a variable frequency drive 304 configured to drive an electricmotor 305, a controller 310, and voltage and current sensors 315.Variable frequency drive 304 includes a first-phase inverter leg 320, asecond-phase inverter leg 325, a third-phase-inverter leg 330, a firstDC bus 335 and a second DC bus 340. The first-phase inverter leg 320 hasan upper switching element 345 and a lower switching element 350, bothof which are electrically connected in a series relationship between thefirst DC bus 335 and the second DC bus 340. The second-phase inverterleg 325 has an upper switching element 355 and a lower switching element360, both of which are electrically connected in a series-typerelationship between the first DC bus 335 and the second DC bus 340. Thethird-phase inverter leg 330 has an upper switching element 365 and alower switching element 370, both of which are electrically connected ina series-type relationship between the first DC bus 335 and the secondDC bus 340. The inverter legs 320, 325, and 330 described above are alsoreferred to as inverter branches. In other embodiments various otherinverter configurations are used.

Electric motor 305 is illustrated as a three-phase electric motorconnected in a wye configuration, however, other configurations such asdelta configuration are also possible. A first phase winding 375 ofmotor 305 is connected between the upper and lower switching elements345 and 350. A second phase winding 380 of motor 305 is connectedbetween the upper and lower switching elements 365 and 370. A thirdphase winding 385 of motor 305 is connected between the upper and lowerswitching elements 355 and 360.

Each lower switching element 350, 360, and 370 includes a transistor 390which, in the illustrated embodiment, is an insulated gate bipolartransistor (IGBT) having a collector coupled to a respective upperswitching element 345, 355, or 365 and an emitter coupled to the secondDC bus 340. Each lower switching element 350, 360, and 370 also includesa diode 395 having a cathode coupled to the respective upper switchingelement 345, 355, or 365, and an anode coupled to the second DC bus 340.The upper switching elements 345, 355, and 365 each include a respectivediode 400 having an anode coupled to the respective lower switchingelements 350, 360, and 370, and a cathode coupled to the first DC bus335. Each of the upper switching elements 345, 355, and 365 include atransistor 405 (e.g., an IGBT) having an emitter connected to therespective lower switching element 350, 360, and 370, and a collectorcoupled to the DC bus 335.

The switching elements 345, 350, 355, 360, 365, and 370 are controlledby the controller 310 to turn the motor 305. In the construction shown,the sensors 315 sense the current through each of the windings 375, 380,385 and the terminal voltage at each of the motor terminals and providesan indication of the sensed current and voltage to the controller 310.The controller 310 powers the windings 375, 380, and 385 to rotate themotor 305. The controller 310 chooses which phase windings to powerbased on the voltage readings sensed by the voltage sensor. Duringoperation, the controlled turning on and off of the switches causes themotor to rotate in a forward direction, resulting in the motor 305driving the compressor 105.

With reference to FIG. 4 there is illustrated an exemplary controlprocess 401 for opposing, limiting, and/or preventing undesired and/orun-commanded compressor rotation. Process 401 begins at conditional 410which evaluates whether a compressor idle condition exists. This may beperformed by evaluating the physical state of the compressor, forexample, identifying a non-rotating or stationary state, identifying thephysical or electrical state of the motor, for example, identifying anon-rotating or stationary state physical or electrical state,evaluating the state of the electrical drive configured to drive themotor, for example, identifying when a control state or command isconfigured not to operate the drive, or through combinations of thesetechniques and/or other techniques. If conditional 410 evaluates false,process 401 returns to conditional 410 which repeats.

If conditional 410 evaluates true, process 401 proceeds to conditional420. Conditional 420 evaluates whether an undesired and/or un-commandedrotation condition risk is present. This may be accomplished with avariety of techniques. Certain techniques evaluate the pressure upstreamof the compressor. Certain techniques evaluate the pressure downstreamof the compressor. Certain techniques evaluate the pressure differentialacross the compressor. Certain techniques evaluate pressure and/ortemperature conditions at other system locations. Certain techniquesevaluate environmental conditions associated with a risk of undesiredcompressor rotation. Such techniques include, for example, detectingrotation of the compressor or of the rotor of the motor with one or moresensors, detecting back EMF potential (or current induced by the same)at the motor terminals which also indicates rotations, or detectinginformation of other system parameters predetermined to be associatedwith a risk of undesired or un-commanded compressor rotation. Certaintechniques utilize combinations of the aforementioned and/or othertechniques.

Regardless of the particular information or parameters utilized toassess risk of an undesired and/or un-commanded rotation condition,conditional 420 may be configured to compare the information orparameters to one or more criteria to identify a risk of undesiredcompressor rotation. This may be accomplished using a variety oftechniques including, for example, look up tables, thresholdcomparisons, computational techniques, statistical techniques, otherpredictive techniques, or combinations of these and/or other techniques.If conditional 420 evaluates false, process 401 returns to conditional410.

If conditional 420 evaluates true, process 401 proceeds to operation 430which commands an operation to oppose, limit, and/or prevent undesiredcompressor rotation. Operation 430 may comprise a number of techniques.In certain embodiments, operation 430 may control a power supply such asa drive to provide a closed circuit or short circuit condition effectiveto dissipate current induced by motor rotation to oppose rotation of amotor coupled with a compressor. In certain embodiments the closed orshort circuit condition may be provided by commanding two or moreswitches, such as two or more of switches 345, 350, 355, 360, 365, and370, to a close configuration to provide a short circuit to a driverail, such as rail 335 or 340 including two or more motor windings, suchas two or more of motor windings 375, 380 and 385.

In certain other embodiments operation 430 may control a power such as adrive to provide a DC current to a motor effective to urge the motortoward a predetermined configuration effective to oppose, limit, and/orprevent undesired compressor rotation. For example, with reference toFIG. 3, controller 310 could command switching elements 345 and 325 toclose providing a closed circuit DC bus rail 335, through motor windings380 and 385 and to DC bus rail 340. A variety of other closed circuitconfigurations involving different combinations of switches and motorwindings may also be employed.

FIG. 5 provides a graphical illustration of one approach for startingcompressor 110. This approach does not include any particular aspectdirected to any liquid clearing function in order to avoid damage tocompressor 110 and/or other components of system 100. Further, inillustrated form, compressor 110 includes liquid which has not beenremoved therefrom before this approach is implemented. Upon activationof compressor 110, current 530 of motor 170 has an initial start profilethat forms a peak 515 at 200 ARMS, although other values are possible.This initial start profile of current 530 is predetermined, and allowsVFD 155 to determine its speed and rotor position. Following peak 515,current 530 of motor 170 undergoes a small decrease as operation ofmotor 170 is switched to follow speed command 520. In order to achievespeed 510 of motor 170 over a set period of time that generallycorresponds to the speed trajectory of speed command 520 provided bycontroller 160, the current 530 of motor 170 undergoes a spike event540. Spike event 540 occurs, in part, due to the relatively high amountof torque that motor 170 must create in order to drive the collectedliquid(s) from compressor 110 so that speed 510 of motor 170 maygenerally meet or correspond to the speed trajectory of speed command520. Controller 160 controls operation of variable frequency drive 155in order to provide motor 170 with the necessary voltage and/or PWMdrive signal required to create sufficient torque of motor 170 to clearcollected liquid(s) and otherwise increase speed 510 of motor 170 tomatch the speed trajectory of speed command 520.

In the illustrated form, the relatively high amount of torque of motor170 in the presence of collected liquid(s) also causes deformation ordeflection of components of compressor 110. More particularly, event 550is representative of a torque induced deformation or deflection of arotor of compressor 110 such that it rubs against the sides of thecompression chamber of compressor 110. The interference betweencomponents at event 550 slows the increase of speed 510 of motor 170,causes a deviation of speed 510 from the speed trajectory of speedcommand 520 around event 550, and also contributes to spike event 540.As would be appreciated by those skilled in the art, spike event 540 canresult in failure or increased susceptibility to failure of one or morecomponents of system 100, including for example compressor 110 and/ormotor 170. In addition, the deformation or deflection of components ofcompressor 110, including those associated with event 550, can result infailure or reduced lifespan of compressor 110.

Turning now to FIGS. 6 and 7, further details of an alternative approachfor starting compressor 110 will be provided. As will be discussed ingreater detail below, this approach provides a liquid clearing functionand controller 160 may be configured to automatically implementperformance of this approach each time compressor 110 is started or inresponse to determining the presence of collected liquid(s) incompressor 110. For forms where this approach is performed in responseto determining the presence of collected liquid(s) in compressor 110, itshould be understood that an alternative approach for operatingcompressor 110 may be performed if the presence of collected liquid(s)in compressor 110 is not determined. For example, and withoutlimitation, the approach for operating compressor 110 at start-upassociated with FIG. 5, where the speed trajectory of speed command 520is the controlling parameter of the operation of compressor 110 atstart-up, may be implemented if the presence of collected liquid(s) incompressor 110 is not determined.

In one form, a sensor or other detection means associated withcompressor 110 is configured to provide a signal to controller 160indicative of the presence or absence of collected liquid(s) incompressor 110, and controller is 160 is responsive to this signal toimplement the appropriate approach for operation of compressor 110 atstart-up. In certain forms, the sensor or other detection means isconfigured to provide the signal indicative of the presence or absenceof collected liquid(s) in compressor 110 to controller 160 beforecompressor 110 is started. Similarly, it should be appreciated thatcontroller 160 may be configured to select and/or implement theappropriate approach for operation of compressor 110 at start-up beforecompressor 110 is started. In another form, the presence of collectedliquid(s) in compressor 110 is determined if the torque of motor 170exceeds a predetermined value within a predefined period of timefollowing start-up of compressor 110. Torque of motor 170 may bemeasured by any suitable means including appropriately configuredsensors. In one particular but non-limiting form, torque of motor 170 isbased upon measured current of motor 170 as torque and current of motor170 are generally directly proportional to one another at low speeds ofmotor 170. In one form, the current value used for determining torque ofmotor 170 is measured simultaneously with the activation of motor 170.

Controller 160 is configured to switch from one approach for operatingcompressor 110 to another approach for operating compressor 110 if thetorque of motor 170 exceeds the predetermined value within thepredefined period of time. By way of non-limiting example, controller160 may be configured to initially start compressor 110 using theapproach illustrated and described in connection with FIG. 5 and thenswitch to the approach associated with FIGS. 6 and 7 if the torque ofmotor 170 exceeds the predetermined value within the predefined periodof time. Similarly, it should be appreciated that a slight delay mightexist after start-up of compressor 110 before the approach associatedwith FIGS. 6 and 7 is implemented. Alternatively, controller 160 may beconfigured to initially start compressor 110 using the approachassociated with FIGS. 6 and 7 and then switch to the approach associatedwith FIG. 5 for example if the torque of motor 170 does not exceed thepredetermined value within the predefined period of time. In one form,the predetermined value for torque of motor 170 corresponds to knowntorque values for motor 170 measured upon activation of compressor 110when compressor 110 is started without any liquid(s) collected therein.

In the approach associated with FIGS. 6 and 7, controller 160 isconfigured to operate compressor 110 in a first or start-up mode whichprevents motor 170 from exceeding a predetermined current limit 660unless speed 670 of motor 170 exceeds predetermined speed threshold 680at or before time 690. In one form, predetermined current limit 660corresponds to a maximum current rating for motor 170 during operationof compressor 110 with the speed of motor 170 at or under the speed ofpredetermined speed threshold 680 in order to avoid damage or potentialdamage to compressor 110. Controller 160 is configured to controloperation of variable frequency drive 155 such that motor 170 isprovided with an appropriate voltage and/or PWM drive signal thatprevents current 600 of motor 170 from exceeding limit 660 before time690 regardless of the torque required of motor 170 in order to makespeed 670 of motor 170 correspond to or meet the speed trajectory ofspeed command 610. In response to speed 670 exceeding predeterminedspeed threshold 680 at or before time 690, controller 160 is furtherconfigured to operate compressor 110 in a second mode or run mode whichgenerally does not limit or prevent current 600 of motor 170 fromexceeding predetermined current limit 660. In the event speed 670 ofmotor 170 does not exceed predetermined speed threshold 680 at or beforetime 690, controller 160 is further configured to stop operation ofcompressor 110.

With more particular reference to FIG. 6, where the values for currentlimit 660, speed threshold 680, and time 690 are non-limiting andexemplary only, current 600 of motor 170 has an initial start profilethat forms a peak 605 at 200 ARMS upon activation of compressor 110.This initial start profile of current 600 is predetermined, and allowsVFD 155 to determine its speed and rotor position. Other variations inthe initial start profile of current 600 are possible. Following peak605, current 600 of motor 170 undergoes a small decrease as operation ofmotor 170 is switched to a mode which prevents motor 170 from exceedingpredetermined current limit 660 unless speed 670 of motor 170 exceedspredetermined speed threshold 680 at or before time 690. Current limit660 is set to limit current of motor 170 from exceeding 200 ARMS beforetime 690. In this manner, speed 670 of motor 170 initially increases andthen holds steady at about 250 RPM generally between times 620 and 630.During this period of time, speed 670 of motor 170 remains relativelylow and facilitates the steady clearance of liquid(s) from compressor110 without the creation of relatively high motor torque or motorcurrent. As a result, damage or failure of compressor 110, motor 170 orone or more other components of system 100 as discussed above inconnection with the approach associated with FIG. 5 may be avoided.Following clearance of liquid(s) from compressor 110 around time 630,speed 670 of motor 170 increases until it generally matches orcorresponds to the speed trajectory of speed command 610. Further,shortly after time 630, current 600 of motor 170 decreases as speed 670of motor 170 increases.

Referring more particularly to FIG. 7, current 600 of motor 170 has aninitial start profile that forms a peak 615 at 150 ARMS upon activationof compressor 110. This initial start profile of current 600 ispredetermined, and allows VFD 155 to determine its speed and rotorposition. Other variations in the initial start profile of current 600are possible. Following peak 605, current 600 of motor 170 undergoes asmall decrease as operation of motor 170 is switched to a mode whichprevents motor 170 from exceeding predetermined current limit 660 unlessspeed 670 of motor 170 exceeds predetermined speed threshold 680 at orbefore time 690. Current limit 660 is set to limit current of motor 170from exceeding 150 ARMS before time 290. It should be understood thatthe values for current limit 660, speed threshold 680, and time 690 inFIG. 7 are non-limiting and exemplary only, and while different fromthose set forth in FIG. 6 could correspond to those set forth in FIG. 6.

In FIG. 7, speed 670 of motor 170 initially spikes to above 1,000 RPM asmotor current 600 reaches current limit 660 and then quickly dives toaround 200 RPM between time 625 and time 635. The initial spike in speed670 of motor 170 is noise which controller 160 can be configured todisregard or filter. After time 635, speed 670 of motor 170 begins toincrease but does not exceed speed threshold 680 set at 600 RPM at orbefore time 690, which represents the end of a six second period of timefollowing start of compressor 160. In response to the failure of speed670 of motor 170 to exceed speed threshold 680 at or before time 690,operation of compressor 110 is stopped. After being stopped, it iscontemplated that one or more restarts of compressor 110 could beattempted after passage of a predetermined period of time, or anindication could be provided to an operator of system 100 to manuallydrain compressor 110 or take other actions to clear liquid(s) fromcompressor 110. Alternatively, controller 160 may be further configuredto automatically activate opening of a drain valve on compressor 110 ortake other liquid clearing action(s) in the event speed 670 of motor 170does not exceed speed threshold 680 at or before time 690. It shouldalso be appreciated that, in addition to or in lieu of implementing theapproach associated with FIGS. 6 and 7, controller 160 may be configuredto implement one or more of these actions upon determining the presenceof liquid(s) in compressor 110 as discussed above.

As mentioned above, controller 160 can be configured to disregard orfilter the initial spike in speed 670 of motor 170 so that the same isnot considered to be a speed of motor 170 above speed threshold 680 ator before time 690 that is necessary to prevent stopping operation ofcompressor 110. For example, in one form controller 160 may beconfigured to disregard speed 670 of motor 170 until some predeterminedtime after current 600 of motor 170 reaches current limit 660 and/or ifspeed 670 of motor 170 is decreasing as is the case following theinitial spike of speed 670, each of which would exclude consideration ofthe initial spike of speed 670 of motor 170. Alternatively, controller160 could disregard speed 670 of motor 170 until a predetermined periodof time has passed following starting of compressor 110 where the periodof time is calculated to exclude the initial spike of speed 670. Still,another approach for disregarding this initial spike of speed 670 mayinvolve controller 160 being additionally or alternatively configured todetermine that speed 670 of motor 170 has exceeded speed threshold 660once speed 670 has been consistently maintained above speed threshold660 for a certain period of time. It should be appreciated however thatother approaches are possible for eliminating or disregardingconsideration of the initial spike of speed 670 of motor 170.

Turning now to FIG. 8, further details of an alternative approach forstarting compressor 110 will be provided. As will be discussed ingreater detail below, this approach provides a liquid clearing functionand controller 160 may be configured to automatically implementperformance of this approach each time compressor 110 is started or inresponse to determining the presence of collected liquid(s) incompressor 110. For forms where this approach is performed in responseto determining the presence of collected liquid(s) in compressor 110, itshould be understood that an alternative approach for operatingcompressor 110 may be performed if the presence of collected liquid(s)in compressor 110 is not determined. For example, and withoutlimitation, the approach for operating compressor 110 at start-updescribed in connection with FIG. 5 may be implemented if the presenceof collected liquid(s) in compressor 110 is not determined.

In one form, a sensor or other detection means associated withcompressor 110 is configured to provide a signal to controller 160indicative of the presence or absence of collected liquid(s) incompressor 110, and controller is 160 is responsive to this signal toimplement the appropriate approach for operation of compressor 110 atstart-up. In certain forms, the sensor or other detection means isconfigured to provide the signal indicative of the presence or absenceof collected liquid(s) in compressor 110 to controller 160 beforecompressor 110 is started. Similarly, it should be appreciated thatcontroller 160 may be configured to select and/or implement theappropriate approach for operation of compressor 110 at start-up beforecompressor 110 is started. In another form, the presence of collectedliquid(s) in compressor 110 is determined if the torque of motor 170exceeds a predetermined value within a predefined period of timefollowing start-up of compressor 110. Torque of motor 170 may bemeasured or determined as discussed herein above, and controller 160 isconfigured to switch from one approach for operating compressor 110 toanother approach for operating compressor 110 if the torque of motor 170exceeds the predetermined value within the predefined period of time. Byway of non-limiting example, controller 160 may be configured toinitially start compressor 110 using the approach illustrated anddescribed in connection with FIG. 5 and then switch to the approachassociated with FIG. 8 if the torque of motor 170 exceeds thepredetermined value within the predefined period of time. Similarly, itshould be appreciated that a slight delay might exist after start-up ofcompressor 110 before the approach associated with FIG. 8 isimplemented. Alternatively, controller 160 may be configured toinitially start compressor 110 using the approach associated with FIG. 5and then switch to the approach associated with FIG. 5 for example ifthe torque of motor 170 does not exceed the predetermined value withinthe predefined period of time. In one form, the predetermined value fortorque of motor 170 corresponds to known torque values for motor 170measured upon activation of compressor 110 when compressor 110 isstarted without any liquid(s) collected therein.

In the approach associated with FIG. 8, controller 160 is configured tooperate compressor 110 to follow a speed command 840 provided bycontroller 160 which includes a speed trajectory that is configured toprevent speed 850 of motor 170 from exceeding a predetermined limit 800from initial starting at time 860 to time 820. In this approach,controller 160 is configured to control operation of variable frequencydrive 155 such that motor 170 is provided with an appropriate voltageand/or PWM drive signal that allows or facilitates speed 850 of motor170 to generally match or correspond to the speed trajectory of speedcommand 840. A current limit 880 is also set for current 890 of motor170 and controller 160 is configured to stop operation of compressor 110if current 890 exceeds limit 880 before time 820. In certain forms,controller 160 may also be configured to stop operation of compressor110 if current 890 exceeds limit 880 after time 820.

With more particular reference to FIG. 8, where the values for currentlimit 880, speed limit 800, and time 820 are non-limiting and exemplaryonly, current 890 of motor 170 has an initial start profile that forms apeak 895 at 200 ARMS upon activation of compressor 110. This initialstart profile of current 890 is predetermined, and allows VFD 155 todetermine its speed and rotor position. Other variations in the initialstart profile of current 890 are possible. Following peak 895, current890 of motor 170 decreases briefly as operation of motor 170 is switchedto a mode configured to operate compressor 110 following speed command840. In addition, current limit 880 is set to 225 ARMS. Between time 860and time 810 the speed trajectory of speed command 840 initiallyincreases from 0 RPM to the speed of speed limit 800. In the illustratedform, the speed of speed limit 800 is about 300 RPM, although it shouldbe appreciated that other variations are possible. The speed trajectoryof speed command 840 maintains constant at the speed of speed limit 800from time 810 to time 820, and then increases over time up to about1,500 RPM. In the illustrated form, times 810 and 820 generallycorrespond to about 1 and 6 seconds, respectively, after time 860,although other variations are possible.

While not previously discussed, it should be understood that the speedtrajectory of speed command 840 will facilitate a clearing function ofliquid(s) in compressor 110. More particularly, the operation ofcompressor 110 following the speed trajectory of speed command 840 willgenerally provide relatively low motor speeds between times 810 and 820that facilitate clearance of liquid(s) from compressor 110 whileavoiding undesirable and increased motor torque and current. Similarly,damage or failure of compressor 110, motor 170 and/or one or more othercomponents of system 100 as discussed above in connection with theapproach associated with FIG. 2 may be avoided. In particular, bylimiting speed 850 of motor 170 until clearance of liquid(s) fromcompressor 110 is achieved, excessive torque and motor current areavoided. However, in the event current 890 of motor 170 should exceedcurrent limit 880, controller 160 is configured to stop operation ofcompressor 110.

While not previously discussed, it should be understood that the speedtrajectory of speed command 840 between times 810 and 820, and thelength of the period of time between times 810 and 820, are selected toprovide clearance of liquid(s) from compressor 110 by time 820. Forexample, these values could be known based on experimentation, orcalculated in light of various factors such as compressor size amongstothers. In one form, the speed trajectory of speed command 840 betweentimes 810 and 820, and the length of the period of time between times810 and 820 are determined based on known values for the volume of freespace in compressor 110, the volume of the compression chamber ofcompressor 110, and a rate at which refrigerant leaks back intocompressor 110. Using these values, a speed can be determined that willnot result in damage to compressor 110, and that speed may be used todetermine the number of rotations (and thus time) necessary to removeliquid(s) from compressor 110.

In addition to the above, while speed 850 of motor 170 exceeds speedlimit 800 in the illustrated form, it should be understood that thespeed trajectory of speed command 840 is nonetheless configured toprevent speed 850 of motor 170 from exceeding speed limit 800 untilafter time 820. Further, in other non-illustrated forms, the speedtrajectory of speed command 340 may remain constant between times 810and 820 at a speed that is below a targeted speed limit in order toaccount for any upward creep that may occur to speed 850 of motor 170between times 810 and 820. As a corollary, forms in which the approachassociated with FIG. 8 prevents speed 350 of motor 170 from exceeding apredetermined speed limit are also possible.

In certain embodiments, a controller is described performing certainoperations to detect and report the reverse rotation of a compressor, orother operations. In certain embodiments, the controller forms a portionof a processing subsystem including one or more computing devices havingmemory, processing, and communication hardware. The controller may be asingle device or a distributed device, and the functions of thecontroller may be performed by hardware or software.

Certain operations described herein include operations to interpret oneor more parameters. Interpreting, as utilized herein, includes receivingvalues by any method known in the art, including at least receivingvalues from a datalink or network communication, receiving an electronicsignal (e.g., a voltage, frequency, current, or a Pulse-Width Modulation(“PWM”) signal) indicative of the value, receiving a software parameterindicative of the value, reading the value from a memory location on acomputer readable medium, receiving the value as a run-time parameter byany means known in the art, and/or by receiving a value by which theinterpreted parameter can be calculated, and/or by referencing a defaultvalue that is interpreted to be the parameter value.

With reference to FIG. 9 there is illustrated an exemplary HVACR system900 which includes a refrigerant loop comprising screw or scroll typecompressors 910, 911, a condenser 920, and an evaporator 930.Refrigerant flows through system 900 in a closed loop from compressors910, 911 to condenser 920 to evaporator 930 and back to compressors 910,911. Various embodiments may also include additional refrigerant loopelements including, for example, valves for controlling refrigerantflow, refrigerant filters, economizers, oil separators and/or coolingcomponents and flow paths for various system components.

Screw or scroll compressor 910 is driven by a drive unit 950 including apermanent magnet electric motor 970 which is driven by a variablefrequency drive 155. In the illustrated embodiment, variable frequencydrive 955 is configured to output a three-phase PWM drive signal, andmotor 970 is a surface magnet permanent magnet motor. Use of other typesand configurations of variable frequency drives and electric motors suchas interior magnet permanent magnet motors, reluctance motors, orinductance motors are also contemplated. Screw or scroll compressor 911is driven by a drive unit 951 including a permanent magnet electricmotor 971 which is driven by a variable frequency drive 956. In theillustrated embodiment, variable frequency drive 956 is configured tooutput a three-phase PWM drive signal, and motor 971 is a surface magnetpermanent magnet motor. Use of other types and configurations ofvariable frequency drives and electric motors such as interior magnetpermanent magnet motors, reluctance motors, or inductance motors arealso contemplated. It shall be appreciated that the principles andtechniques disclosed herein may be applied to a broad variety of driveand motor configurations, systems and subsystems including those furtherdescribed herein below. It shall be further appreciated that the sameapplies to a number of additional or alternate controllers, controlmodules or control units, including but not limited to those describedelsewhere herein.

Condenser 920 is configured to transfer heat from compressed refrigerantreceived from compressor 910. In the illustrated embodiment, condenser920 is a water cooled condenser which receives cooling water at an inlet921, transfers heat from the refrigerant to the cooling water, andoutputs cooling water at an output 922. It is also contemplated thatother types of condensers may be utilized, for example, air cooledcondensers or evaporative condensers. It shall further be appreciatedthat references herein to water include water solutions comprisingadditional constituents unless otherwise limited.

Evaporator 930 is configured to receive refrigerant from condenser 920,expand the received refrigerant to decrease its temperature and transferheat from a cooled medium to the refrigerant. In the illustratedembodiment evaporator 930 is configured as a water chiller whichreceives water provided to an inlet 931, transfers heat from the waterto the refrigerant, and outputs chilled water at an outlet 932. It iscontemplated that a number of particular types of evaporators may beutilized, including dry expansion evaporators, flooded type evaporators,bare tube evaporators, plate surface evaporators, and finned evaporatorsamong others.

HVACR system 900 further includes a controller 960 which outputs controlsignals to variable frequency drives 955, 956 to control operation ofmotors 970, 971 and compressors 910, 911. Controller 960 also receivesinformation about the operation of drive units 950, 951. In exemplaryembodiments controller 960 receives information relating to motorcurrent, motor terminal voltage, and/or other operationalcharacteristics of the motor. It shall be appreciated that the controls,control routines, and control modules described herein may beimplemented using hardware, software, firmware and various combinationsthereof and may utilize executable instructions stored in anon-transitory computer readable medium or multiple non-transitorycomputer readable media. It shall further be understood that controller960 may be provided in various forms and may include a number ofhardware and software modules and components such as those disclosedherein below.

With reference to FIG. 10, an example embodiment of a system 700 usedfor detecting a reverse rotation of a compressor, which may be used in aHVACR system, is provided. As shown, the system 700 may be provided witha power supply 702, which may be a mains power supply, such as describedhereinabove, coupled to a controller 704, which may be coupled to avariable frequency drive 706 or components thereof, which is coupled toan electric motor 707, which is mechanically coupled to and configuredto drive a compressor 708, which may be a screw or scroll compressor.The compressor 707 is designed to run or operate in one direction, whichmay be designated as a forward direction, with the opposite directionbeing a reverse direction. The reverse direction being one that subjectsthe compressor to potential damage.

The exemplary controller 704 is provided with several modules 710, 720,730, 740, 750 structured to perform various tasks to detect and stopreverse rotation of a compressor 708. The controller is provided with asupply module 710 that is coupled to a power supply 702 and a variablefrequency drive 706. The supply of power 703 flows from the power supply702 to the supply module 710. The supply module 710 is structured toselectively or selectably feed power 705 to the variable frequency drive706 to start the motor 707. The supply module 710 may do this bylimiting the amount of current, voltage, or alter the frequency of thepower 705. During normal operation, the supply module 710 may feed asupply of power 705, which may be a continuous supply, to the variablefrequency drive 706. Thus, the supply module is structured to start themotor 707. The supply module 710 is also configured to interrupt thepower supply to the variable frequency drive 706, and in turn the motor707. The act of interrupting the power supply may include terminatingthe supply of current, especially when the controller 704 detects thatthe compressor 708 is operating in reverse.

The example controller 704 is also provided with a current detectionmodule 720 that is structured to receive an input from a sensor anddetect and determine an amount of current 725 drawn by the electricmotor 706. It is appreciated that this feedback or drawn current value725 is different than the line current being fed to the motor 707 viathe supply module 710. The current detection module 720 may incorporatevarious detection sensors as are known in the art, which may or may notbe incorporated as part of the variable frequency drive 706. Asdiscussed hereinafter, there may likely be an initial current spike inthe drawn current value at startup of the motor 706 and compressor 708.Therefore, the current detection module 720 may be structured such as toignore this initial current spike, or to not begin monitoring the drawncurrent until after this initial current spike in drawn current hassubsided. This may be done by not monitoring or ignoring the monitoreddrawn current until a predetermined time after the commencement ofsupplying current. It is further appreciated that the current detectionmodule may detect any number of characteristics of the drawn current,such as, for example: a maximum characteristic, such as a currentmagnitude, which may be a summed or integrated current; an instantaneousrate of change or current; or a current differential.

The example controller 700 is further provided with a threshold module730 that is structured to interpret and/or determine a drawn currentthreshold value 735. The drawn current threshold value 735 may be storedas a predetermined value from a memory location on a computer readablemedium. Such a location may be in the controller 700 itself, and may beincorporated into the threshold detection module 730, or any othermodule associated with the controller 700. The drawn current thresholdvalue 735 is a value that may be determined empirically for a givencombination of motor 707 and compressor 708, and the determination ofwhich will be described hereinafter. It is appreciated that the drawncurrent threshold value 735 may be any characteristic of the drawncurrent, but may specifically be a limit of the characteristic of thatdetected by the current detection module 720, which may be, for example:a maximum characteristic limit, such as a current magnitude limit, whichmay be a summed or integrated current; a limit of an instantaneous rateof change of current; or a current differential limit.

The controller 700 may be provided with a diagnostic module thatdetermines a health value 745 associated with the motor 706 andcompressor 708 combination. The health value is determined by comparingthe drawn current value 725 to the drawn current threshold value 735 todistinguish between normal compressor operation and a current conditionattributable or indicative of compressor reverse rotation. Should thedrawn current value 725 be less than the drawn current threshold value735, then the health value 745 passes. Should the drawn current value725 be greater than or equal to the drawn current threshold value 735,then the health value 745 fails.

The example controller 700 is also provided with a control module 750that is structured to interpret the health value 745 and send a “go/nogo” signal to the supply module 710 in response to the health value 745.If the health value 745 passes, then the control module 750 sends a “go”signal to the supply module 710 an all operations proceed as normal. Ifthe health value 745 fails, then the control module 750 sends a “no go”signal to the supply module 710 and power 705 is cut to the motor 706and all operations cease before the compressor 708 can be damaged.

Referring now to FIGS. 11 and 12, example graphs are provided for twodifferent motor and compressor combination assemblies detailing themotor drawn current value, the velocity command, and velocity feedbackover time. The motor drawn current value is the drawn current value 725as described herein, the velocity command is the velocity at which themotor is directed to rotate, and the velocity feedback is actualmeasured velocity at which the motor is rotating. As shown in FIGS. 11and 12, an initial spike in motor drawn current is expected upon startupof the motor and compressor assembly. It is after this initial startupspike that the effects of motor reverse rotation are seen in the motordrawn current value. The motor draws an abnormal amount of current dueto the increase torque load on the motor to keep up with the velocitycommand. The current drawn by the motor is proportional to the amount oftorque that it produces.

Referring to FIG. 11, a motor and compressor combination has an initialstartup current spike of approximately 100 amps that ends atapproximately 1.5 to 2 seconds after the initial startup. Afterapproximately 2 seconds after startup commencement, the motor drawncurrent value increases with the velocity command within normal limits.It is at approximately 4 seconds after startup that the effects of motorreverse rotation are apparent in the motor drawn current value. As thecompressor rotates in reverse, especially for screw and scrollcompressors, the internal parts begin to interfere and/or grindtogether, which generates heat that may lead to the welding of internalcompressor components, and irreparable damage to the compressor.

For the motor and compressor combination of FIG. 11, the drawn currentthreshold value may be set at approximately 150 to 200 amps. This meansthan when the motor drawn current meets or exceeds this value, the motorwould be signaled to shut down or power would be cut off to stop themotor and prevent any damage from being done to the compressor. Thisvalue of 150 to 200 amps is above the 100 amps drawn at startup andwould not stop the motor and compressor assembly during a normalstartup.

It is worth noting that the motor and compressor assembly of FIG. 11 waslimited to 300 amps. Therefore, the motor drawn current value did notexceed that value. The test was also only run for approximately 8.5seconds after initial startup. Had the system 300 of the presentdisclosure been utilized in this test, with a drawn current thresholdvalue of either 150 or 200 amps, the motor and compressor assembly wouldhave ceased to rotate at approximately 4 seconds after startup.

Referring to FIG. 12, a motor and compressor combination has an initialstartup spike of approximately 200 amps that ends at approximately 1second after the initial startup commencement. After approximately 1second after startup, the motor drawn current value increases with thevelocity command within normal limits. It is at just under 9 secondsafter startup that the effects of motor reverse rotation are apparent inthe motor drawn current value.

For the motor and compressor combination of FIG. 12, the drawn currentthreshold value may be set at approximately 300 amps. This means thanwhen the motor drawn current meets or exceeds this value, the motorwould be signaled to shut down or the power supply would be interruptedto stop the motor and prevent any damage from being done to thecompressor. This value of 300 amps is above the 200 amps drawn atstartup and above the approximately 250 amps that the motor draws duringthe velocity ramp up. This 300 amp drawn current threshold value wouldnot stop the motor and compressor assembly during a normal startup, butit would stop the motor and compressor assembly prior to any damagebeing done. The test was run for approximately 12.5 seconds afterinitial startup. Had the system 300 of the present disclosure beenutilized in this test, with a drawn current threshold value ofapproximately 300 amps, the motor and compressor assembly would haveceased to rotate at approximately 9 seconds after startup.

The previous examples of a reverse running compressor illustrate how thedrawn current threshold value can vary depending on the motor andcompressor combination. Several factors are utilized to determine thedrawn current threshold value, they may include any one or more of thefollowing: the rated current of the motor; the rated torque of themotor; the inertia of the compressor; the desired velocity (velocitycommand) and/or acceleration (ramp up of velocity command) of thecompressor; and the anticipated velocity feedback. Accordingly, becausethese factors take into account properties of both the motor, thecompressor, and the desired performance of the combination, the drawncurrent threshold value may be unique to each motor and compressorcombination and its application and may be verified with empiricaltesting.

It is also appreciated that many characteristics of the drawn currentvalue may be determined from the graphs of FIGS. 11 and 12. Thesecharacteristics may be, for example: a maximum characteristic, such as acurrent magnitude, which may be a summed or integrated current; aninstantaneous rate of change; or a current differential.

Another factor to take into consideration is time. As shown in FIGS. 11and 12, an initial current spike in drawn current during the startup isnormal, but can lead to a false alarm that the compressor is running inreverse. Therefore, the system and methods described herein mayselectively ignore this initial startup spike in drawn current and notbegin to monitor the drawn current until a predetermined amount of timehas lapsed after system startup. As shown in FIGS. 4 and 5, this may beafter 1 to 2 seconds have passed after startup. Again, this initial timeto ignore depends upon the motor and compressor combination that isutilized in the system and further depends on the factors discussed inthe preceding description.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinventions are desired to be protected. It should be understood thatwhile the use of words such as preferable, preferably, preferred or morepreferred utilized in the description above indicate that the feature sodescribed may be more desirable, it nonetheless may not be necessary andembodiments lacking the same may be contemplated as within the scope ofthe invention, the scope being defined by the claims that follow. Inreading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary. Unless specified or limitedotherwise, the terms “mounted,” “connected,” “supported,” and “coupled”and variations thereof are used broadly and encompass both direct andindirect mountings, connections, supports, and couplings. Further,“connected” and “coupled” are not restricted to physical or mechanicalconnections or couplings.

It shall be further understood that the exemplary embodiments summarizedand described in detail above and illustrated in the figures areillustrative and not limiting or restrictive. Only the presentlypreferred embodiments have been shown and described and all changes andmodifications that come within the scope of the invention are to beprotected. It shall be appreciated that the embodiments and formsdescribed below may be combined in certain instances and may beexclusive of one another in other instances. Likewise, it shall beappreciated that the embodiments and forms described below may or maynot be combined with other aspects and features disclosed elsewhereherein. It should be understood that various features and aspects of theembodiments described above may not be necessary and embodiments lackingthe same are also protected. In reading the claims, it is intended thatwhen words such as “a,” “an,” “at least one,” or “at least one portion”are used there is no intention to limit the claim to only one itemunless specifically stated to the contrary in the claim. When thelanguage “at least a portion” and/or “a portion” is used the item caninclude a portion and/or the entire item unless specifically stated tothe contrary. Unless specified or limited otherwise, the terms“mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

The invention claimed is:
 1. A system comprising: a refrigerant circuitincluding a compressor configured to compress refrigerant, a condenserconfigured to receive refrigerant from the compressor, and an expanderconfigured to receive refrigerant from the condenser; an electric motorconfigured to drive the compressor; a motor drive configured to drivethe electric motor; and a controller configured to control the motordrive to drive the electric motor; wherein the controller is configuredto first evaluate whether the compressor is idle based upon a controlstate of the controller being configured not to operate the motor driveto drive the motor, second, in response to an affirmative evaluationthat the compressor is idle, evaluate a risk of undesired orun-commanded compressor rotation based upon a combination of two or moresystem conditions, each of the two or more system conditions indicatingthe risk of undesired or un-commanded compressor rotation, and third, inresponse to an affirmative evaluation of the risk of undesired orun-commanded compressor rotation, control the motor drive to opposerotation of the compressor.
 2. The system according to claim 1 whereinthe controller being configured to control the motor drive to opposerotation of the compressor comprises the controller being configured tocontrol the motor drive to close two or more switching devices toprovide a closed circuit condition effective to provide an electricalresistance of the motor to current generated by rotation of the motor.3. The system according to claim 2 wherein the closed circuit conditioncomprises providing a closed circuit including two or more windings ofthe motor and a rail of the motor drive.
 4. The system according toclaim 1 wherein the controller being configured to control the motordrive to oppose rotation of the compressor comprises the controllerbeing configured to control the motor drive to provide a DC current tothe motor effective to urge the motor to a predetermined alignment andresist rotation of the motor.
 5. The system according to claim 1 whereinone of the of two or more system conditions comprises a pressuredifferential across the compressor associated with risk of undesired orun-commanded compressor rotation.
 6. The system according to claim 1wherein one of the of two or more system conditions comprises a pressurecondition associated with risk of undesired or un-commanded compressorrotation.
 7. The system according to claim 1 wherein the motor drivecomprises an inverter.
 8. The system according to claim 1 wherein themotor drive comprises a variable frequency drive.
 9. The systemaccording to claim 1 wherein the condition associated with risk ofundesired or un-commanded compressor rotation comprises rotation of arotor of the motor.
 10. The system according to claim 1 wherein thecondition associated with risk of undesired or un-commanded compressorrotation comprises rotation of the compressor being detected with asensor.
 11. The system according to claim 1 wherein the conditionassociated with risk of undesired or un-commanded compressor rotationcomprises back EMF indicative of rotation being detected at a motorterminal.
 12. The system of claim 1 wherein the two or more systemconditions include detection of one of a potential and a current at themotor terminals and detection of a pressure condition associated withthe compressor.
 13. A method comprising: providing a system comprising arefrigerant circuit including a compressor configured to compressrefrigerant, a condenser configured to receive refrigerant from thecompressor and an expander configured to receive refrigerant from thecondenser, an electric motor configured to drive the compressor, a motordrive configured to drive the electric motor, and a controllerconfigured to control the motor drive to drive the electric motor;operating the controller to first evaluate whether the compressor isidle based upon a control state of the controller being configured notto operate the motor drive to drive the motor; operating the controllerto second, in response to an affirmative evaluation that the compressoris idle, evaluate a risk of undesired or un-commanded compressorrotation based upon a combination of two or more system conditions, eachof the two or more system conditions indicating the risk of undesired orun-commanded compressor rotation; and operating the controller to third,in response to an affirmative evaluation of the risk of undesired orun-commanded compressor rotation, control the motor drive to opposerotation of the compressor.
 14. The method of claim 13 wherein the actof operating the controller to control the motor drive to opposerotation of the compressor comprises operating the controller to controlthe motor drive to close two or more switching devices to provide aclosed circuit condition effective to provide an electrical resistanceof the motor to current generated by rotation of the motor.
 15. Themethod of claim 14 wherein the closed circuit condition comprisesproviding a closed circuit including two or more windings of the motorand a rail of the motor drive.
 16. The method of claim 13 wherein themotor drive comprises an inverter.
 17. The method of claim 13 whereinthe motor drive comprises a variable frequency drive.
 18. The method ofclaim 13 wherein the condition associated with risk of compressorrotation comprises rotation of a rotor of the motor when compressorrotation is not commanded.